The innovation pertains to a ventilation device for a piston for a cartridge.
According to DE GM 298 00 594, a micropore filter is inserted into a pocket formed in the piston. By means of this micropore filter, the air trapped between the filling mass and the piston can escape when the piston is inserted into the cartridge. Furthermore, this micropore filter is to prevent emission of the filling mass. With the bearing of the cartridges, components of certain filling masses exhibit a creeping, oil-like behavior. These components penetrate the micropore filter, which leads to leakage.
DE GM 295 06 800 shows another ventilation device. Here, the ventilation is performed by means of a plurality of valve plugs mounted around a divided circle of the piston cover, and these plugs are lifted from valve cones when the piston is pressed into the cartridge, thus enabling the outlet of air. However, this ventilation device can only be manufactured with tight production tolerances. Another disadvantage can be seen in that parts of the filling mass can advance up to the valves, which are then contaminated, so that their sealing function is adversely affected.
Starting with this ventilation device, the task is to configure this device such that the valve remains dry and free of dirt. Creeping, oil-like components of the filling masses should be prevented from leaking from the valve.
The invention relates to a ventilation device for a piston for a cartridge, comprising a first piston part which rests sealingly against the cartridge wall and a second piston part, which forms a valve together with the first piston part. Said valve opens when a pressure is exerted on the rear side of the piston so that the air is trapped between the filling composition and the piston can escape. According to the invention, a filter section is provided in front of the valve, between the two piston parts, as seen from the flow path of the air through the valve. This filter section has at least one narrow channel which forms a penetration barrier for the filling mass and ensures that the valve remains dry and free of dirt.